1. Technical Field of the Invention
The present invention relates to promoting desquamation of the skin and/or stimulating epidermal renewal and/or combating aging of the skin by topical application thereto of cinnamic acid or derivative thereof, or composition comprising same.
The compounds/compositions of this invention are especially well suited for promoting desquamation of the skin and/or stimulating epidermal renewal and/or combating intrinsic and/or extrinsic aging of the skin, as well as for nontherapeutically treating the skin to promote desquamation and/or combat aging of the skin.
2. Description of the Prior Art
Desquamation is a natural phenomenon associated with the fact that the epidermis, which constitutes the upper layer of the skin, is in constant regeneration. The epidermis consists of several layers of cells, the deepest of which is the basal layer consisting of undifferentiated cells. These cells differentiate and migrate towards the surface of the epidermis over time, constituting the various layers thereof, until they form at the surface of the epidermis the corneocytes, which are dead cells, which are removed by desquamation. This loss of surface is compensated for by the migration of cells from the basal layer towards the surface of the epidermis. This entails perpetual renewal of the skin. Forced removal of the horny layer accelerates the renewal and makes it possible to combat aging.
At the same time, these cells continue their differentiation, the final stage of which is the corneocyte. These are dead cells which make up the final layer of the epidermis, namely, the outermost layer also known as the stratum corneum.
Aging of the skin resulting from the effects of intrinsic or extrinsic factors on the skin is reflected by the appearance of wrinkles and fine lines, by yellowing of the skin which develops a parchment-like appearance accompanied by the appearance of pigmentation blemishes, by the disorganization of the elastin and collagen fibers, causing a loss of elasticity, flexibility and firmness, and by the appearance of telangiectases.
Certain of these signs of aging are more particularly associated with intrinsic or physiological aging, namely, with “normal” aging due to age or chronobiological aging, whereas others are more specific to extrinsic aging, namely, aging caused in general by the environment; this relates more particularly to photoaging due to exposure to sunlight, to light or to any other radiation, whether natural or artificial.
The present invention relates to not only intrinsic or physiological aging, but also to extrinsic aging.
The changes in the skin due to intrinsic aging are the consequence of a genetically programmed senescence involving endogenous factors. This intrinsic aging causes, in particular, a slowing down or retarding of the renewal of the skin cells, which is reflected essentially by the appearance of clinical impairments such as reduction in the subcutaneous adipose tissue and the appearance of small wrinkles or fine lines, and by histopathological changes such as an increase in the number and thickness of elastic fibers, a loss of vertical fibers from the membrane of the elastic tissue, and the presence of large irregular fibroblasts in the cells of this elastic tissue.
By contrast, extrinsic aging causes clinical impairments such as large wrinkles and the formation of a flaccid and weathered skin, and histopathological changes such as excessive accumulation of elastic material in the epidermis and degeneration of the collagen fibers.
Various active agents suggested for combating aging of the skin are known in the prior art.
Thus, U.S. Pat. No. 4,603,146 describes the use of retinoic acid and derivatives thereof in cosmetic compositions for combating skin aging.
Moreover, many patents and publications (see, for example, EP-A-413,528) describe, and numerous commercially available commercial cosmetic compositions include, α-hydroxy acids, such as lactic acid, glycolic acid or citric acid, for treating aging of the skin.
Too, the β-hydroxy acids, and more especially salicylic acid and derivatives thereof, are known for their desquamating properties (see WO-A-93/10756 and U.S. Pat. No. 4,767,750).
All of the aforesaid prior art compounds elicit action against aging of the skin by promoting desquamation, i.e., the removal of the “dead” cells located at the surface of the horny layer of the epidermis. This “desquamating” property is also referred to, often incorrectly, as a keratolytic property.
However, the compounds of the prior art also present objectionable side effects, such as stinging, tautness and sensations of overheating and redness which are unpleasant for the user.
Need therefore continues to exist for antiaging agents having an action which is at least as effective as that of the compounds of the prior art, but which do not present the disadvantages thereof.